REAL-TIME SYSTEMS II Real-Time Networking Wireless sensor networks Prof. J.-D. Decotignie CSEM Centre Suisse d’Electronique et de Microtechnique SA Jaquet-Droz 1, 2007 Neuchâtel [email protected]2011, J.-D. Decotignie Real-Time Networks – Wireless Sensor Networks 2 2011, J.-D. Decotignie Real-Time Networks – Wireless Sensor Networks 3 Motes, BT nodes, Smart-Its, Cyclope, … 2011, J.-D. Decotignie Real-Time Networks – Wireless Sensor Networks 4 Outline Characteristics of wireless transmission Features of wireless sensor networks Medium access control schemes for WSNs WiseMAC Comparison with other protocols Conclusion
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REAL-TIME SYSTEMS IIReal-Time NetworkingWireless sensor networks
Prof. J.-D. DecotignieCSEM Centre Suisse d’Electronique et de
Outline Characteristics of wireless transmission Features of wireless sensor networks Medium access control schemes for WSNs WiseMAC Comparison with other protocols Conclusion
MAC master-slave (switching time longer timeouts) bus arbiter (hidden node limitation in broadcast, reliable
detection of silence BA redundancy) tokens (hidden node token loss, switching time longer timeouts) virtual token (reliable detection of silence token passing) CSMA (no collision detection use timeouts) TDMA (switching time longer gaps)
Possible architectures single or multiple wireline segments single or multiple wireless cells single or multiple points of connection connection through repeater, bridge, router or gateway ad hoc (self organising) wireless cell or base station single hop / multiple hops use of satellites
WSN expected features self organized no infrastructure (no base station, etc.) battery operated (low energy) multihop transmission small (< 1cm3), low cost (target <0.5$) low data rate (up to 10 Kbit/s/node) large number of nodes (0.05 to 1 nodes/m2) sensor information temporal consistency
7 myths about wireless transmission the world is flat a radio transmission area is circular all radios have equal range if I can hear you, you can hear me if I can hear you at all, I can hear you perfectly signal strength is a simple function of distance link quality does not change
WiseMAC Req. & Assumptions Designed for the WiseNET System-on-a-chip
FSK Radio, 2 mA RX, 800 s setup time, 35 mA TX, 5 W DOZE SoC operates down to 0.9V to require a single battery 8 bits CoolRisc C, little memory available
Target lifetime of years on a single AA alkaline battery Multi-hop, Low average data rate, High latencies tolerated
AA alkaline battery• 2.6 Ah • Power leakage of 27 W
WiseMAC Based on Synchronized CSMA with Preamble Sampling
Preamble sampling to minimize consumption of idle listening wake-up preamble minimized by exploiting knowledge of sampling schedule of
direct neighbors, less transmit, receive & overhearing overheads. No setup-signalling. Self local synchronisation and re-synchronization Choice of TW is a trade-off between energy and latency
Sampling schedule information inserted in every ack. Clocks drift of at most ± per second (typically =30 ppm) With L seconds in between two communications, the length
‘More’ Bit ‘More’ bit in data header indicates follow-up packets Allows the transport of busty traffic with low delays Cost of wake-up preamble shared among several
First Conclusions WiseMAC is a single channel contention MAC protocol based
on synchronized CSMA with preamble sampling No setup-signalling. Self local synchronisation and re-
synchronisation. Adaptive to traffic: ultra-low power consumption in low traffic
conditions and high energy efficiency in high traffic condition Supports sporadic, periodic and bursty traffic Provides years of autonomy with a single AA alkaline battery
under traffic loads up to 1 message every 10 seconds 2011, J.-D
Infrastructure Based Wireless Sensor Network Sensor nodes communicate with access points Access points are connected to an infrastructure network Access points are energy unconstrained Examples:
Temperature monitoring in an office building, using Ethernet infrastructure
Alarm system at home, using Powerline infrastructure Solar powered or vehicle mounted access points
Low Power MAC Protocols To save energy, the radio of sensor nodes must be
turned off when not communicating. MAC protocol should minimize idle listening,
overhearing and collisions.How to wake-up sensor nodes for receiving traffic ?
Base station is energy unconstrained May listen to the channel all the time. May transmit any amount of data and signaling traffic.How to exploit the unlimited energy at the base station to save energy at the sensor node ?
Sensor nodes sample the medium to detect a wake-up preamble. Access points send wake-up preamble in front of data packets. APs learn the sampling schedule of sensor nodes (through ACK
messages) & send messages at the right time, with a wake up preamble of minimized size.
References J.-D. Decotignie et al. « Architectures for the interconnection of wireless and
wireline fieldbusses », Proc. FeT 2001, Nancy, Nov. 15-16, pp.285-290 J.-D. Decotignie, « Wireless fieldbusses - a survey of issues and solutions »,
In Proc. 15th IFAC World Congress on Automatic Control (IFAC 2002), Barcelona, Spain, 2002.
A. El-Hoiydi, J.-D. Decotignie, « WiseMAC: An Ultra Low Power MAC Protocol for Multi-hop Wireless Sensor Networks », In Proc. ALGOSENSORS 2004, LNCS 3121, pp. 18-31. Springer-Verlag, July 2004.
Amre El-Hoiydi et al., « Low Power MAC Protocols for Infrastructure Wireless Sensor Networks », In Proc. European Wireless (EW'04), pages 563-569, Barcelona, Spain, Feb. 2004.
Philippe Morel, « Intégration d'une liaison radio dans un réseau industriel », Thèse EPFL, no 1571 (1996).
K. Langendoen and A. Meier. « Analyzing MAC protocols for low data-rate applications ». ACM Trans. Sen. Netw. 7, 1, Article 10 (August 2010), 34 p.
Reference (cont.) W. Ye et al. « Medium Access Control With Coordinated Adaptive Sleeping for
Wireless Sensor Networks », IEEE/ACM Trans. on Networking, vol. 12, issue 3, June2004, pp. 493- 506
W. Ye, et al., “An energy-efficient MAC protocol for wireless sensor networks”, in INFOCOM 2002, pp. 1567-76, June 2002.
A. El-Hoiydi, « Energy efficient medium access control for wireless sensornetworks », PhD thesis, EPFL, Lausanne, 2005
G. P. Halkes, T. van Dam, K. G. Langendoen , “Comparing Energy-Saving MAC Protocols for Wireless Sensor Networks”, Mobile Networks and Applications, volume 10, issue 5, october 2005, pp. 783 - 79
Research in CH: www.mics.org D. Kotz et al.. “The mistaken axioms of wireless-network research”, Dartmouth
College CS Technical Report TR2003-467, July 18, 2003 Rousselot, J.; El-Hoiydi, A.; Decotignie, J.-D.; “Low power medium access control
protocols for wireless sensor networks, 14th European Wireless Conf, pp.1-5, 2008. R. Serna Oliver, Gerhard Fohler. Timeliness in Wireless Sensor Networks: Common
Misconceptions. In Proceedings of the 9th International Workshop on Real-Time Networks (RTN2010), Brussels, Belgium, July 2010.